By Lester Holt, NBC News anchor

There are an awful lot of people sitting in airports and hotels, far from home today because they've been told it's not safe to fly home.  For all the well known frustrations of air travel these days, a verifiable threat to safety -- in this case a volcanic ash capable of snuffing out a jet engine -- will usually quiet even the most disgruntled passenger. Now, for the first time since the closure of European airspace we are starting to see some push back.  Not from passengers, but from the airlines themselves.

Some European carriers have been re-positioning empty jets and running test flights, and discovering there has been no damage to their jets.  The CEO of British Airways even went along on one such test flight apparently to make a point.  Many airline officials are openly wondering whether aviation authorities over-reacted to the threat posed by the drifting ash plume, and prematurely closed airports.

Experts acknowledge tracking an ash cloud is not a perfect science.  Which of course leads to the question how will we know when it is safe to fly? Does a successful flight today guarantee a successful flight tomorrow along the same route? And, how does the airline industry balance an abundance of caution against the reality of staggering financial losses and a public clamoring to get back into the air?

On our broadcast tonight, in addition to our reporting from the base of the volcano in Iceland, and airports in Europe, I'll be speaking with a former NTSB chairman about how authorities will navigate these difficult questions.

I hope you can join me later for NBC Nightly News.